A wide variety of nucleic acid amplification methods are available, and many have been employed in the implementation of sensitive diagnostic assays based on nucleic acid detection. Polymerase chain reaction (PCR) remains the most widely used DNA amplification and quantitation method. Nested PCR, a two-stage PCR, is used to increase the specificity and sensitivity of the PCR (U.S. Pat. No. 4,683,195). Nested primers for use in the PCR amplification are oligonucleotides having sequence complementary to a region on a target sequence between reverse and forward primer targeting sites. However, PCR in general has several limitations. PCR amplification can only achieve less than two fold increase of the amount of target sequence at each cycle. It is still relatively slow. In addition, the sensitivity of this method is typically limited, making it difficult to detect target that may be present at only a few molecules in a single reaction.